By what entity and over what time frame are API request limits counted?

I’ve been looking over the documentation on API Request Limits so I can do large imports while ensuring I don’t overcome the limit, but I realized there’s some information missing from the documentation.

Namely, against what are these limits counted – corporate account, user account, or IP address? Also, is the limited counted as an average for the month, or is it simply a minute-to-minute timeout? While I don’t foresee it happening, if my application were to hit our limits, I want to make sure we won’t be stuck for the rest of the month, and if so, that it tracks overall API requests. Similarly, how I track it on my end (per user, altogether, etc) depends on how it’s counted on your end.